This invention relates to an apparatus and method for drying damp powders of fragile, low density materials. Drying of particulate and powdered materials is a step common to many manufacturing processes, and special techniques have been developed suited to production of individual products.
Characteristics of the end product, for example, whether the material is agglomerated or separated, control the method of drying. Considerable difficulty has been encountered in drying damp powders, such as glass bubbles and expanded perlite, which are fragile and have a low, real or apparent, density. The dried product must be a free-flowing powder substantially composed of unfractured individual particles and/or agglomerates as the process may require. Attempts to do this by conventional methods, for example, flash drying, fluid bed reactors and rotary calciners, have been unsuccessful and unsuitable. Commercial flash driers have too low a residence time for materials to be dried in the drying media; fluid bed reactors are ineffective with low density materials because of bed segregation, over agglomerating, and difficulty in control of operating parameters. Rotary kilns produce clinkers and large agglomerates which must be removed from the product, and the end product does not flow freely. Commercial spray driers do not have the required residence time due to the air flow patterns of these devices.
What is needed is an economic process which dries damp powdered materials, particularly those of low density, to produce a lightweight free-flowing product comprised of unfractured particles.